1. Field of the Invention
The present invention relates to polybenzoxazole resins which are excellent in electrical characteristics, thermal characteristics, and mechanical characteristics, and which are usable as layer insulation films and protective films for semiconductors, layer insulation films of multilayer circuits, cover coats of flexible copper-clad sheets, solder resist films, liquid crystal-aligned films, etc.
2. Related Art Statement
Among the characteristics required for insulation materials for semiconductors, electric characteristics, particularly, dielectric constant and heat resistance are most important characteristics. In order to allow these two characteristics to be compatible with each other, organic insulation films of high heat resistance are expected. For example, inorganic insulation films such as silicon dioxide which have hitherto been used, have a high heat resistance, but are high in dielectric constant, and the two characteristics are hardly compatible with each other. Organic insulation films represented by polyimide resins are excellent in electric characteristics and heat resistance and have compatibility in the two characteristics, and are actually used as solder resists, cover layers, liquid crystal-aligned films, and the like.
However, with recent enhancement in function and performance of semiconductors, remarkable improvement of electric characteristics and heat resistance is needed, and resins of further higher performances are demanded. Particularly, those materials are expected which have a low dielectric constant of 3.0 or lower and which have a glass transition point (Tg) of 400.degree. C. or higher. As to polyimide resins, it has been also attempted to attain the above properties, for example, by introducing fluorine and trifluoromethyl group into the high molecules, but at present the properties have not yet reached the desired level.
Among resins other than polyimide resins, polybenzoxazole resins are expected. The presence of two carboxyl groups in the imide ring of polyimide resins adversely affect electric characteristics. In general polybenzoxazole resins are essentially superior to polyimide resins in electric characteristics, and hence it is easy to allow heat resistance and dielectric constant to be compatible with each other. However, the level of electric characteristics required is very high and the conventional polybenzoxazole resins have not reached the required level.